1. Field of the Invention
Embodiments of the present invention relate to a media access control (MAC) protocol of a wireless local area network (WLAN), and more particularly, to a configuration of a frame for use in frame transmission based on uplink multi-user multiple-input and multiple-output (MU-MIMO) technology.
2. Description of the Related Art
Recently, in wireless communication systems, a multiple-input and multiple-output (MIMO) technology for transmitting and receiving data using at least two antennas is being generalized. A wireless local area network (WLAN) also enables at least two transmission antennas to be used from the Institute of Electrical and Electronics Engineers (IEEE) 802.11n standard. The IEEE 802.11n standard allows for use of up to four antennas, and the IEEE 802.11ac standard allows for use of up to eight antennas. For example, in a case of using a great number of transmission antennas, data transmission may be performed based on transmit beamforming technology, thereby improving a performance of signal reception.
For efficient use of frequency resources, the IEEE 802.11ac for which standardization is in progress may include downlink multi-user multiple-input and multiple-output (MU-MIMO) technology enabling an access point (AP) to simultaneously transmit beamformed data frames to a plurality of stations (STAs). Also, research is being conducted into uplink (UL) MU-MIMO technology enabling transmission of data frames to the AP from the plurality of STAs and reception of the data frames at the AP through being separated for each stream, to be conducted simultaneously.
FIG. 1A illustrates an example of an operation in which at least two STAs transmit data to an AP according to a related art. An STA 1 and an STA 2 may initiate a random backoff when a channel is in an idle state. In FIG. 1A, the STA 1 terminating the random backoff earlier than the STA 2 may transmit a data frame 1 to the AP, and receive a first acknowledge (ACK) frame. Since the STA 2 listens to frames transmitted by the STA 1, the STA 2 may standby in a state of suspending the random backoff. When the ACK frame ends, the STA 2 may continue the random backoff, and transmit a data frame 2 to the AP.
FIG. 1B illustrates an example of an operation in which at least two STAs transmit data to an AP based on UL MU-MIMO technology according to a related art.
Similar to the operation of FIG. 1A, an STA 1 and an STA 2 may initiate a random backoff when a channel is in an idle state. The STA 1 terminating the random backoff earlier than the STA 2 may transmit, to the AP, a data frame 1 on which beamforming is performed. Due to the beamforming, the STA 2 may not listen to the data frame 1. Thus, the STA 2 may process the random backoff without suspending transmission, and transmit a data frame 2 on which beamforming is performed to the AP.
When the data frame 2 is received during reception of the data frame 1, a physical (PHY) layer of the AP may abnormally perform data reception. Based on a known research result, UL MU-MIMO frames may need to be temporally synchronized within an error range of less than 100 nanoseconds (ns) to receive data.
Accordingly, UP MU-MIMO data reception may not be performed using an existing method.